I'm finding that Avast AV Free and Internet Security 2013 do a real good job, comparable performance to the big guys (Norton and McAfee; both of which I run on my machines and my Client business machines). Avast IS 2013 is about 1/2 the first-time purchase cost AND on the annual subscription cost compared to Norton & McAfee. I've been using Anti-Virus programs since 1980 back in the days of FPROT (before Windows was around) so I have some experience there.
Norton & McAfee are up to charging $60 a year for their subscriptions, and Avast is around $25-$50; depending on when they are having special deals. I have a Customer who just got a 2-year deal on their Avast IS for $60; so $30 a year; 1/2 the price of the big guys. And I have had Customers running Norton AND McAfee bring me in their severely disabled computers with the FBI Ransomware virus even when they are running their top of the line proudcts and are completely updated! After switching a Client with an infected computer that slipped through Norton or McAfee, I have had no repeat infestations. After all, 184 Million people run Avast now worldwide, I think that's a statement.
I believe Avast is somewhere around #3 or #4 in the U.S. quality-wise and gaining market-share fast. Don't what the marketing guys have to say about sales statistics; but, if you are going to pay for professional quality protection, but your computer is still catching mass-infection malware, you have to wonder what you or your Client's are paying for.
For the Corporate IT types reading this, Avast certainly doesn't have the inroads into Enterprise Security like CA type products costing thousands, and Norton & McAfee still do the best job with the big corporate networks, but don't be surprised if you seem them soon!
I've deployed Avast now on about 25 client machines or so since 2012, and am very impressed indeed. I highly recommend their products for pay-level protection. If you are insisting on using a Free AV product or anti-spyware or anti-malware; my current model is to deploy between 4-6 Malware products running in the background as a 2nd line of defense to the Avast. This has been working well. I also suggest you look at MALWAREBYTES and TREND MICRO, who have very strong products which are both free.
My 2 cents.
Cheers!
BIGBEARJEDI